Upregulation of p21WAF1/Cip1 precedes tumor necrosis factor-induced necrosis-like cell death

The molecular mechanisms mediating death receptor-induced caspase-independent necrotic cell death are still largely unknown. We have previously reported that NIH3T3 cells are sensitized by caspase inhibition to death receptor-induced cytotoxicity leading to a necrosis-like cell death. In addition, we have identified an important role of cell cycle progression for this sensitization effect. Here, we report that tumor necrosis factor-induced necrotic death is preceded by an upregulation of the cyclin-dependent kinase inhibitor p21WAF1/Cip1. Increased expression of p21WAF1/Cip1 occurs prior to cell death in the nucleus, where it binds to a cyclin-dependent kinase indicating its functionality. The use of specific pharmacological inhibitors revealed a partial involvement of p38 mitogen-activated protein kinase in the upregulation of p21WAF1/Cip1. Inhibition of p21WAF1/Cip1 upregulation prevents a previously observed delay of the cells in the G2/M phase of the cell cycle thereby augmenting, not inhibiting cell death.